Synchronous electric motor

ABSTRACT

A polyphase synchronous A C motor having rectangular wave power input includes a stator having axially spaced core members, a D. C. winding between the core members and a polyphase winding extending through the core members. The rotor has two squirrel cage sections, one aligned within each core member and each squirrel cage section carries a pole piece. Each pole piece has a pair of diametrically opposed radially projecting poles and the poles of one pole piece are displaced 90* with respect to the poles of the other pole piece. The motor has a total of four circumferentially spaced poles and thus presents a pole pitch of 90* for each phase. The polyphase winding has at least one winding per phase. In one embodiment the poles have a circumferential width ( 90*) equal to the pole pitch and the polyphase windings have a like circumferential width. In another embodiment the poles have a circumferential width ( 60*) which is two-thirds of the pole pitch and, again, the polyphase windings have a like circumferential width.

Ulllted States Patent 1 1111 3,732,448

Schiethart May 8, 1973 1 SYNCHRONOUS ELECTRIC MOTOR 3,535,572 10 1970DeRugeris ..310 1s5 3,510,699 5 1970 Fredrickson ..310 114 [75] InventLodew'lk schethan Dubbeldam 3,169,203 2/1965 Lavin ..310/162 Netherlands[73] Assignee: N.V. Electromotorenfabriek Dordt, Primary ExaminerflR-Skudy Dordrecht, Netherlands Attorney-Snyder and Butrum [22] Filed: Apr.6, 1971 ABSTRACT Continuation-in-part of Ser. No. 2,195, Jan. 12, 1970,Pat. No. 3,614,496.

Foreign Application Priority Data Apr. 22, 1970 Netherlands ..70/05797[52] US. Cl ..310/162, 310/211 [51] Int. Cl. ..H02k 12/00 [58] Field ofSearch ..3l0/l62, 163, 164, 310/165, 179, 180,183,185, 187, 216, 218,212, 213, 214, 264, 265, 114,113, 112; 318/138 [56] References CitedUNITED STATES PATENTS 3,171,049 2/1965 Jarrett ..310/ll4 3,560,8202/1971 Unnewehrm; ..3l0/163 A polyphase synchronous A C motor havingrectangular wave power input includes a stator having axially spacedcore members, a D. C. winding between the core members and a polyphasewinding extending through the core members. The rotor has two squirrelcage sections, one aligned within each core member and each squirrelcage section carries a pole piece. Each pole piece has a pair ofdiametrically opposed radially projecting poles and the poles of onepole piece are displaced 90 with respect to the poles of the other polepiece. The motor has a total of four circumferentially spaced poles andthus presents a pole pitch of 90 for each phase. The polyphase windinghas at least one winding per phase. In one embodiment the poles have acircumferential width 90) equal to the pole pitch and the polyphasewindings have a like circumferential width. In another embodiment thepoles have a circumferential width 60) which is two-thirds of the polepitch and, again, the polyphase windings have a like circumferentialwidth.

4 Claims, 5 Drawing Figures PATENTEU MAY 8 I975 SHEET 1 BF 3 INVENTOR lo06 w/JIr .rc/ms r/Mw A ENTEH 8 3; 732,448

SHEET 2 UF 3 INVENTOR PATENTEUKAY 81913 SHEET 3 OF 3 stutor core3-phuse-winding phase I Poles of other rotorhult are 90 degreesdisplaced (tangential) FIG.5

SYNCHRONOUS ELECTRIC MOTOR CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of my copending application Ser.No. 2,195 filed Jan. 12, 1970 claiming priority of Dutch application No.69.0084 of Jan. 17, 1969 which copending application is now US. Pat. No.3,614,496 issued Oct. 19,1971.

The invention relates to a synchronous electric motor comprising astator provided with a polyphase winding and a winding for producing acoaxial d.c. field and a rotor whose poles are disposed in two axiallyspaced transverse planes.

In a motor of this type, it is desirable that the form of the voltageinduced by the poles in the polyphase winding should correspond as faras possible to that of the supply voltage. If this is not so and onevoltage, for example, is a square wave and the other a sine wave, higherharmonic compensating currents will form and produce an extra powerconsumption. If the motor is under load, the compensating current incomparison with the total current is relatively smaller than in the zeroload condition. In processes, for example, in the textile industry, inwhich the motors operate under zero load conditions for a relativelyconsiderable part of the operating time, the compensating current willconstitute a relatively high percentage of the total current and thetotal power consumption is therefore adversely affected.

One solution of this problem would be to adapt the form of the supplyvoltage, but this would require complicated steps which would increasethe costs. The above problem arises particularly when the motor issupplied from static frequency converters. In the simplest construction,a converter of this type delivers a square-wave voltage.

The object of the invention is to provide a motor of the above describedtype which can be supplied with a square-wave voltage and which producesonly minor compensating currents under zero-load conditions.

To this end, according to the invention, the pole width is substantiallyequal to the pole pitch. This results in a motor in which a square-wavevoltage can be produced in the polyphase winding. The above step canreadily be put into effect in a motor in which the poles are disposed inaxially spaced planes in comparison with a motor in which this is notthe case. In a motor in which the poles are situated in one plane, itwould be impossible to carry out the step according to the invention,because the rotor poles would be in contiguous relationship and thepoles could not then be referred to as separate poles. The problem doesnot arise, however, in a motor in which the poles are situated indifferent axially spaced planes. The step according to the inventiongives the greatest advantage in a motor in which the polyphase windingis constructed with one groove per pole and per phase.

As a second solution for achieving the object according to theinvention, the pole width can be approximately two-thirds of the polepitch, in which case the polyphase winding is constructed with two coilsper groove, and the width of each coil is reduced by onethird withrespect to the pole pitch.

The invention will be explained in detail with reference to a drawingillustrating one exemplified embodiment.

FIG. 1 is a longitudinal section through a motor with four polesaccording to the invention;

FIG. 2 is a perspective view of the rotor of the motor according to theinvention;

FIG. 3 is a section on the line IIIIII in FIG. 1 and FIG. 4 is alongitudinal section of a variant; and

FIG. 5 is a cross section illustrating-that embodiment wherein the polewidth or circumferential breadth is two-thirds of the pole pitch.

The stationary part or stator of the motor includes a substantiallycylindrical housing 1 provided at opposite ends with shields 2 and 3which are connected to the housing 1 by means of bolts 4, 5respectively. The shields 2 and 3 are provided with openings for thepassage of the rotor shaft 6 which is rotatably supported in the shields2 and 3 respectively by ball bearings 7, 8. The latter are closed byrings 9 and 10 respectively. A felt dust seal 11 is provided between thering 9 and the shield 2 and a felt dust seal 12 is provided between thering 10 and the shield 3. That end of the shaft to the left as viewed inthe drawing is provided with a blade wheel 13 which acts as a fan deviceand blade wheel 13 is shielded by a plate 14 which is fastened to thehousing 1 by means of bolts 15. The opposite end of the shaft isprovided with a keyway 16. The dc. winding 17 excites the motor. On bothsides of a space ring member enclosing the winding 17, laminated corestructures 18 and 19 are provided hearing a polyphase winding 20. Thispolyphase winding 20 is composed of coils or groups of coils whosedimensions in the peripheral direction correspond substantially to thepole pitch of different polarity. An alternating or rotating field isproduced by means of this winding 20.

The two end portions of the shaft 6 consist of nonmagnetic materialwhile the intermediate portion 6', which has an enlarged diameter,consists of magnetic material. Laminated poles provided with squirrelcages are mounted on the intermediate portion in two axially spacedplanes. The cage with the bars 27 to the left as viewed in the drawingis bounded axially by rings 30 and 32 respectively, while the bars 27 ofthe righthand squirrel cage terminate in the rings 34 and 36respectively.

Laminations forming a pole are provided between each pair of rings. Eachset of laminations comprises an annular main body portion and one ormore radially projecting portions forming the actual poles 23, 24 and25, 26 respectively. According to the invention, the width of thesepoles is equal to the pole pitch, and this means that the correspondingpoints of a pole in one plane are situated on substantially the sameaxial line as those points of a pole in the other axially offset plane.The poles in one plane are offset by with respect to those in the otherplane.

The outside of the main body of the poles is notched to receive theinner portions of the bars 27 and 27'. The axial width of the polescorrespond to that of the associated core members 18 and 19. A spacerring 22 of magnetic material is mounted between the two poles on theintermediate portion 6' and maintain the required distance between thepoles.

During operation, the concentric exciting winding 17 conducts a directcurrent and produces an axially directed d.c. field in the housing andthe shaft, closing through the core structure of the stator at thepoles. The polarity of the poles depends on the direction of this field.In addition to the above-mentioned low power consumption, particularlyat zero load, an important advantage of the motor is that a controllablefield can be obtained without co-rotating windings and slip rings andbrushes.

FIG. 4, in which'like parts have been given the same reference numeralsas in FIG. 1, illustrates a modification in the arrangement and positionof the exciting winding. Two axially spaced exciting windings l7 and 17are provided laterally of a central common stator core structure 28.Three corresponding poles 24, 25 and 25 are disposed within the threestator core structures, the middle pole 25 and the associated middle,core structure 28 having-a double axial width and hence beingdimensioned for a double flux. Rods 27,

27 and 27' respectively are disposed between the end plates 30/32, 38/40and 34/36. This construction is suitable particularly for higher powersand is to be used whenever the outside diameter of the motor is subjectto limitations. Clearly, a construction with more than three stator corestructures and poles is possible instead of three stator core structuresand poles.

As mentioned, the coils or windings are so constructed as to provide onegroove per pole and per phase. Thus for a three phase system with fourpoles as in FIGS. 1-3, there would be 12 grooves. Moreover, since'thecoils or windings are of the same circumferential width as are thepoles, there will be only one winding associated with each groove inthis embodiment.

If, however, two windings are associated with each groove as is shown inFIG. 5, the pole width or breadth is reduced to two-thirds of the polepitch, as shown. For example, phase I coil a and phase III coil c areassociated with the groove G; phase II coil b and phase III coil areassociated with the groove G and so on for the several phase I, II andIII windings a, a, a, a'; b, b, b", b'; and c, c, c", c, respectively.

What I claim is:

' l. A synchronous A.C. motor comprising, in combination:

a housing having at least a pair of axially spaced core members disposedtherein;

D.C. winding means disposed between said core members for establishing aclosed D.C. magnetic field extending axially within said housing andpassing radially through'said core members;

polyphase winding means extending through said core members andcircumferentially of said housing for establishing a rotating magneticfield within said housing; rotor journalled in said housingconcentrically of said core members and said winding means, said rotorincluding a shaft, squirrel cage winding means fixed to said shaft andincluding circumferentially spaced electrically conducting rods andremote end plates disposed in planes substantially straddling said coremembers, and a pair of pole pieces within the confines of said squirrelcage winding means and each pole piece having a plurality of radiallyprojecting and uniformly circumferentially spaced poles with theradially projecting poles of one pole piece being displacedcircumferentially with respect to the poles of the other pole piece tolie in alignment with the spaces thereof;

said polyphase winding means comprising a plurality of circumferentiallyspaced coils for each phase with each coil having a width in theperipheral direction around said rotor substantially equal to the polepitch and each pole having substantially the same peripheral width asthe coils.

2. A synchronous A.C. motor comprising, in combination:

a housing having at least a pair of axially spaced core members disposedtherein;

D.C. winding means disposed between said core members for establishing aclosed D.C. magnetic field extending axially within said housing andpassing radially through said core members;

polyphase winding means extending through said core members andcircumferentially of said housing for establishing a rotating magneticfield within said housing;

a rotor journalled in said housing concentrically of said core membersand said winding means, said rotor including a shaft, squirrel cagewinding means fixed to said shaft and including circumferentially spacedelectrically conducting rods and remote end plates disposed in planessubstantially straddling said core members, and a pair of pole pieceswithin the confines of said squirrel cage winding means and each polepiece having a plurality of radially projecting and uniformlycircumferentially spaced poles with the radially projecting poles of onepole piece being displaced circumferentially with respect to the polesof the other pole piece to lie in alignment with the spaces thereof;said polyphase winding means comprising a plurality of circumferentiallyspaced coils for each phase with each coil having a width in theperipheral direction around said rotor substantially equal to two-thirdsof the pole pitch and each pole having substantially the same peripheralwidth as the coils. 3. A synchronous motor as defined in claim '1wherein said pole pitch is 4. A synchronous motor as defined in claim 2wherein said pole pitch is 90.

1. A synchronous A.C. motor comprising, in combination: a housing havingat least a pair of axially spaced core members disposed therein; D.C.winding means disposed between said core members for establishing aclosed D.C. magnetic field extending axially within said housing andpassing radially through said core members; polyphase winding meansextending through said core members and circumferentially of saidhousing for establishing a rotating magnetic field within said housing;a rotor journalled in said housing concentrically of said core membersand said winding means, said rotor including a shaft, squirrel cagewinding means fixed to said shaft and including circumferentially spacedelectrically conducting rods and remote end plates disposed in planessubstantially straddling said core members, and a pair of pole pieceswithin the confines of said squirrel cage winding means and each polepiece having a plurality of radially projecting and uniformlycircumferentially spaced poles with the radially projecting poles of onepole piece being displaced circumferentially with respect to the polesof the other pole piece to lie in alignment with the spaces thereof;said polyphase winding means comprising a plurality of circumferentiallyspaced coils for each phase with each coil having a width in theperipheral direction around said rotor substantially equal to thE polepitch and each pole having substantially the same peripheral width asthe coils.
 2. A synchronous A.C. motor comprising, in combination: ahousing having at least a pair of axially spaced core members disposedtherein; D.C. winding means disposed between said core members forestablishing a closed D.C. magnetic field extending axially within saidhousing and passing radially through said core members; polyphasewinding means extending through said core members and circumferentiallyof said housing for establishing a rotating magnetic field within saidhousing; a rotor journalled in said housing concentrically of said coremembers and said winding means, said rotor including a shaft, squirrelcage winding means fixed to said shaft and including circumferentiallyspaced electrically conducting rods and remote end plates disposed inplanes substantially straddling said core members, and a pair of polepieces within the confines of said squirrel cage winding means and eachpole piece having a plurality of radially projecting and uniformlycircumferentially spaced poles with the radially projecting poles of onepole piece being displaced circumferentially with respect to the polesof the other pole piece to lie in alignment with the spaces thereof;said polyphase winding means comprising a plurality of circumferentiallyspaced coils for each phase with each coil having a width in theperipheral direction around said rotor substantially equal to two-thirdsof the pole pitch and each pole having substantially the same peripheralwidth as the coils.
 3. A synchronous motor as defined in claim 1 whereinsaid pole pitch is 90*.
 4. A synchronous motor as defined in claim 2wherein said pole pitch is 90* .